1. Field of the Invention
The present invention relates to a torque sensor using a magnetostrictive member.
2. Description of the Related Art
Torque sensors using stress magnetic properties of a magnetostrictive member to detect changes in torque are commonly known.
One conventional torque sensor 1 shown in FIG. 21, for example, comprises a titanium alloy torque transmission shaft 2 and coils 3A, 3B concentrically wound around the shaft 2. Thin strips 4A, 4B of nickel-iron magnetic material having magnetostrictivity, which have undergone heat treatment to reduce the internal stress, are bonded on the torque transmission shaft 2 under an in-plane compressive stress (see Japanese Patent Laid-Open Publication No. Hei 5-5660).
The torque sensor 1 detects impedance changes of the coils 3A, 3B, which indicate changes in the magnetic properties of the magnetic thin strips 4A, 4B in accordance with torsional stress in the torque transmission shaft 2, to determine changes in the torque of the torque transmission shaft 2.
However, this conventional torque sensor 1 requires a bridge circuit or the like to enhance the detection sensitivity because the changes in the magnetic properties or the magnetostrictivity of the magnetic thin strips 4A, 4B are too small. The cost was accordingly high, and moreover, there was a limit to the improvement of detection sensitivity.